Disk Drives Explained

CowboyRobot writes "Magnetic disk drives are one of those things I usually take for granted without thinking about, but I recently realized how little I understood about how they really work. ACM Queue has an article from their 'Storage' issue titled, 'You Don't Know Jack About Disks', which does a very good job of explaining exactly how magnetic disks have evolved since the 70s and how they work today."

Comments

Re:just in time...

[Anonymous Coward]

Don't you mean Power Glove?

Re:This is a great paper.

[Ella the Cat]

If someone asks me which computer to buy, I'd like to think I could assess their level of technical understanding and their needs in under two hours, provide encouragement, explanation, and make a useful recommendation. Your attitude alienates people.

Magentic disk drives are bad for environment

[Krapangor]

The magenic layers contain very large amounts of chrome-oxides and other heavy metals and rare elements. This makes disk drives a huge problem in the disposal of old computers.
Furthermore the rare element production takes often place in very anarchic countries like Kongo or Liberia. Usually warlords and local terrorists use the money from the disk drives rare elements to finance their blood raids and terrorship.
That's btw the reason why the US were setting up Kabila in Kongo. This guy was killed, but only because the French were more clever.

So, instead of this old technology which is going to be phased out in 5 years anyway, you should use more modern flash/ram disks and DVDs for data storage, just for moralic reasons.
Think about it: If you refuse to buy bananas or big name brands because of the cruel, inhumane exploitation of the third-world workers, then you should do the same in IT and avoid disk drives.

Re:Magentic disk drives are bad for environment

[Reziac]

A LOT of mining, of every sort, takes place in underdeveloped countries. Check out, frex, the issues involved with bauxite mining in the 3rd world (bauxite is the ore from which aluminum is extracted, using vast amounts of electricity in the process. Don't DVDs use an aluminum layer? Doesn't that DVD drive have an aluminum frame?)

Take away the mining industry, and what do you have? A lot of now-unemployed miners with NO other work available, and reduced cash flow in a country that's already strapped, thus making it even harder on their average citizens. This effectively duplicates the situation with Cuba, which hasn't done a thing to improve conditions there. Quite the reverse.

I've seen firsthand what happens when a one-note economy (as most mining-dependent economies are) is shut down: 90% unemployment and long-term economic disaster. Anyone from Butte, Montana, who remembers when the copper mine was shut down, can verify this. Imagine what happens in a country with no support infrastructure for the unemployed.

Re:A bit more history

[Rick.C]

When you consider that the average mainframes of the early '70s had around 512K (yes, "K") of memory (the big ones had a meg or two), you can understand the need to conserve memory. Most programs ran in 60K regions. You just didn't have room for a lot of large data buffers. CKD format allowed you to write whatever size records made sense for your application.

The real beauty of CKD was the "K" or "key" field. If you wrote data blocks with keys, you could then ask the disk controller to search for a given key while your program was executing other code. The controller would find the matching record, read it into storage and interrupt when it was done!

Nowadays most mainframe DASD is really RAID-1 or RAID-5 SCSI arrays that emulate CKD under the covers. With gobs of RAM and the introduction of "dataspaces", the usefulness of CKD is debatable, but like other legacy interfaces, CKD will be a long time dying.

Re:This is a great paper.

[archen]

I've set a few people up with old PII/350's, just to get them a computer in the first place..

I get similar requests about "what computer should I buy" at work, and usually a 350 is about all they need. But I still get "Is this the fastest you can get? Because I don't want to upgrade in 2 years". Well they'll probably upgrade in 2 years anyway or they wont reguardless of speed. So I just recommend they get some computer with an Athlon (not Duron) and that they don't spend more than $650 on it. Most other questions about RAM and disk space are moot because they're enough for most users now days even at the low end, and I don't want to get into explanations they probably won't understand.

If people want really advanced advice I usually only explain that they want a really good power supply, and a good main board (MSI makes pretty decent ones in my experience). Two critical components that no one ever looks at because they're focused on the processor.